This invention relates to an apparatus and method for dewatering an elastomeric polymer. More specifically, the invention is directed to an apparatus and method for dewatering a slurry of water and/or other liquids and elastomeric polymer, (e.g., ethylene propylene diene monomer rubber (EPDM), ethylenepropylene rubber (EPR), butyl rubber, halogenated butyl rubber and the like) in which the slurry is extruded through the barrel of a dewatering extruder, while the extruder conditions are continuously adjusted to provide a predetermined moisture content to the dewatered extrudate based on a real-time measurement of the water or moisture content of the elastomeric polymer within the extruder barrel. By controlling the moisture content of the elastomeric polymer based on the water or moisture content within the extruder barrel, a more efficient process can be achieved, and thus, a superior finished elastomeric polymer product, can be provided.
In the production of elastomeric polymers (or xe2x80x9celastomersxe2x80x9d), water is conventionally used to convey and cool the elastomers after the end of polymerization, as well as to remove excess monomer from the elastomer. A portion of this process water must then be separated or removed from the elastomeric polymer prior to packaging and shipping, separation of the water from the elastomeric polymer is commonly accomplished using an extruder based dewatering and drying process. the elastomeric polymer is commonly accomplished using an extruder based dewatering and drying process.
In separating the water from the elastomeric polymer to form a dewatered or dried product, (referred to as xe2x80x9cbalexe2x80x9d or xe2x80x9ccrumbxe2x80x9d) the advantages of precisely controlling the moisture content of the crumb within the extrusion process are well recognized. Knowing the water content precisely within the extruder or extruders themselves, provides control guidelines or drying temperature requirements, extruder operating capacity, crumb quality (such as porosity, fines, and crumb size distribution). These in turn, control the bale quality such as the residual moisture and friability in the finished product. Friability is important for semi-crystalline elastomeric polymers. A friable bale leads to good dispersion of elastomer in the mixing process such as a Banbury mixer.
Prior attempts to control the moisture content of the elastomer crumb extruded through a dewatering extruder have proven inadequate. One such method involved manually taking a sample of the elastomer/water mixture then subsequent analysis of the withdrawn sample outside the extruder. Japanese Patent Application 59-188082 to Tokuyama Soda Co., Ltd. describes one such process in which the withdrawn sample is formed into a thin sheet and scanned with an infra-red (IR) scanner. Another method involves the analysis of samples collected at the exit port of the dewatering extruder. Such methods are generally not capable of providing sufficiently accurate water content analysis, as the true water content is obscured by the instantaneous release of water that occurs upon exit of the elastomer from the extruder at an elevated temperature and elevated (above atmospheric) pressure. More importantly, such methods can only provide moisture analysis on an in-frequent basis, such as hourly, which in turn further delays any control mechanism.
Therefore, it would be highly desirable to provide a method and apparatus for better controlling the moisture content of an elastomer product that is recovered from an elastomer/water mixture by use of a dewatering extruder process. The present inventors have found that precise and effective control of the moisture content of an elastomer product can be achieved by continuously measuring and instantaneously analyzing the water content of the elastomeric polymer at a point within a dewatering extruder and or a drying extruder and adjusting extruder conditions using a closed loop moisture control system based, at least in part, on the measured water content.
More precise control of elastomeric polymer product moisture content can be achieved by measuring and analyzing the water content of an elastomer/water content at a position within the barrel of a dewatering or drying extruder or both, instantaneously comparing the measured water content of the elastomer/water mixture to a reference value that correlates to a predetermined product moisture content and adjusting extruder conditions (e.g., adjusting the extruder exit die aperture, extruder temperature, initial slurry water content combinations thereof and the like) when the measured elastomer water content differs from the reference or desired value. Due to the fact that the slurry being dewatered is opaque, conventional xe2x80x9ctransmission typexe2x80x9d probes are not acceptable. Instead, a diffuse reflectance type probe, which does not rely on passing a light beam through the material being analyzed, is used.
A method and apparatus is presented for determining the water content of a water/elastomer mixture within the barrel of a dewatering or drying extruder, and using the measured water content to adjust extruder conditions to provide a desired elastomer product moisture content. In a preferred embodiment, the method and apparatus of the invention relates to controlling the moisture content of the elastomer product by determining the water content of the elastomer using a Fourier Transform Near Infrared (FTNIR) spectrometer coupled to a high pressure, diffuse reflectance probe, provided within the barrel of the dewatering or drying extruder.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification and appended claims.